Conventionally, an assembled battery having multiple unit cells coupled in series may have a switch circuit for the electric potential measurement of each of the multiple unit cells by using a single voltage measurement circuit. That is, the switch circuit having a metal-oxide semiconductor field effect transistor (MOSFET) switches a connection between the voltage measurement circuit and each of the unit cell terminals in the multiple unit cells. According to Japanese Patent document 2006-53120 (JP '120) and Japanese Patent 4,450,817 (JP '817), in order to achieve a normal operation of the switch circuit even in a situation where the measurement voltage is higher than a gate-source withstand voltage of the MOSFET, the switch circuit is configured to have two MOSFETs coupled in series for having an electric current directed to a resistor element coupled between the gate and the source of those MOSFETs to turn on the switch circuit.
However, according to JP '120 and JP '817, a unit cell is used as a power supply of the electric current to be directed to the above resistor element. Therefore, a voltage drop occurs by an on-resistance of the MOSFET. Further, a voltage drop also occurs in a resistor in a filter circuit that is used for noise removal, when each of the unit cells has the filter circuit. As a result, the voltage drops may affect the measurement result of the voltage measurement circuit.